This invention relates to organophosphorus compounds, especially organophosphates and organothiophosphates. More particularly, it relates to the electrochemical synthesis of organophosphates and organothiophosphates in compartmented or uncompartmented cells.
Neutral organic esters and thioesters of phosphoric acid have been synthesized in the past by the reaction of phosphurus trichloride and phosphorus oxychloride with alcohols, phenols, mercaptans, or thiophenols. More recently organic phosphates have been prepared by the reaction of phosphorus pentachloride with ethers, as disclosed in U.S. Pat. No. 2,407,279. Employing phosphorus halides to make organic phosphates or thiophosphates generates hydrogen halides as by-products, which are corrosive, difficult to handle, and troublesome to dispose of in an environmentally sound manner. The reaction of phosphorus pentoxide with organic hydroxyl or sulfhydryl compounds required high temperatures, often high pressure, and the maintenance of supplies of reactive chemicals in inventory.
Warshawsky, Tomilov, and Smirnow published in the All-Union Journal of General Chemistry 7, 598 (1962-USSR) a description of an electrochemical process for the synthesis of trialkyl phosphates by passing current between graphite electrodes in a cell containing alcoholic hydrogen chloride and a suspension of red phosphorus. Trimethyl, triethyl, tributyl and triamyl phosphates were made from the respective alcohols by this procedure.
Hettinger disclosed in U.S. Pat. No. 2,079,311 an electrochemical method for preparing tertiary phosphines using an anode of elemental phosphorus. Of the various allotropic forms of phosphorus, black was the preferred phosphorus electrode.
In Electrochemical Technology 45, 502-6 (1966) Barry and Tobias published studies of the anodic oxidation of white phosphorus. In these studies the authors disclose electrodes comprising phosphorus-mercury, phosphorus-silver, phosphorus-platinum, phosphorus-copper, phosphorus-nickel, phosphorus-tin, phosphorus-lead, phosphorus-iron, and amalgams of the above combinations. The preferred phosphorus anode contained graphite powder or silver amalgams.
White disclosed in U.S. Pat. No. 4,021,321 an indirect electrochemical oxidation of phosphorus in aqueous hydrogen halide and an immiscible nonaqueous solvent such as chloroform to produce phosphorus acid.
Dolan disclosed in U.S. Pat. No. 4,021,322 an indirect electrochemical oxidation of phosphorus in aqueous hydrogen halide to produce phosphorus acid.
A principal object of the invention is to produce organophosphorus compounds directly from elemental phosphorus. Another object of the invention is to produce trialkyl phosphates and thiophosphates without generating hydrogen chloride as a by-product. A further object of the invention is to produce organophosphorus compounds at ambient temperatures and pressures. Other objects of the invention will be evident to those skilled in the art from study of the description and examples below.